The ability to view movies (content) in three-dimensions (3D) has existed for decades, mostly limited to movie theater experiences. With the relatively recent availability of 3D-capable consumer-grade television sets, its' use is growing tremendously.
However, many people experience headaches and other adverse symptoms when viewing 3D content. One potential cause is that the 3D content is presented in a way that is not ‘natural’ to the viewer's brain—meaning that some aspect of the appearance of the content is not being accepted by the viewers brain properly.